Precise timing of the fuel charge injection into an engine cylinder (usually measured in relation to the top dead center (TDC) postion of the cylinder operating piston) is a critical factor in maximizing the fuel efficiency of the engine and in minimizing the engine noise level and the pollutant discharge in the engine exhaust. Also, precise regulation of fuel charge injection timing is necessitated by increasing environmental considerations and regulatory mandates. Improved injection timing can be achieved by employing a more precise means for controlling the fuel injection timing and also by employing more engine operation parameters in determining the optimum timing.
In fuel injection pump timing systems having a high degree of precision, the means provided for advancing and retarding the fuel injection timing may be responsive to a control loop which periodically receives an update of the actual fuel injection timing for determining and applying the desired timing adjustment. According to the present invention, increased timing precision is obtained by precisely determining the fuel injection timing at the beginning of each fuel injection event and initiating a corresponding timing adjustment prior to the succeeding fuel injection event.
Fuel charge injection normally occurs when the piston is at or near TDC. The desired time of fuel charge injection varies with the engine design and ranges from slightly prior to TDC to slightly after TDC. Quantification of fuel injection timing is commonly determined and expressed in terms of degrees of crankshaft rotation relative to TDC.
In the normal course of engine operation, various engine operation data or parameters such as engine speed, load, temperature, and altitude or intake manifold pressure may vary sufficiently to require timing adjustments to maintain optimum fuel injection timing. For example, as the engine speed increases, the fuel injection timing should normally occur earlier relative to TDC. That is because the time required for fuel combustion (in terms of crankshaft degrees) increases with engine speed and therefore should be considered in determining the optimum fuel injection timing. Accordingly, the usual fuel injection pump normally employs a mechanism for adjusting the fuel injection timing with engine speed.
Another change in the engine operation which requires a timing adjustment is the change in the engine load or quantity of the injected fuel charge. For example, advancing the fuel injection timing for rapid engine acceleration is generally advantageous. Also, a timing adjustment may be made to compensate for engine temperature. Thus, it is generally advantageous to advance the fuel injection timing in cold engine operation at relatively low speed. A fourth factor for which a compensating adjustment of the fuel injection timing is desirable is the engine altitude for example as measured by the intake manifold pressure. In general, the fuel injection timing should be advanced as the altitude increases or the intake manifold pressure decreases. Other factors, such as pump wear and fuel density, may also require a timing adjustment to obtain optimum timing.
In fuel injection pumps of the type wherein the contour of a cam activates the fuel pressurizing plungers of a charge pump, the fuel injection timing may be controlled by an hydraulically operated timing control piston connected to advance or retard the charge pump timing.
Means for regulating the fuel injection timing by controlling the position of a timing control piston under various engine operating conditions have been devised such as that disclosed in U.S. Pat. No. 4,224,916 of Charles W. Davis, dated Sept. 30, 1980 and entitled "Timing Control for Fuel Injection Pump". The present invention is essentially directed to improvements in determining the timing of the fuel injection event and in reducing the response time for effecting a timing adjustment. In accordance with the present invention, the timing adjustment is preferably implemented by adjusting the position of the timing control piston.
Prior art references disclose methods and systems for measuring the fuel injection timing by either sensing the movement of the fuel injection nozzle valve, sensing an increase in the fuel pressure at the fuel injection nozzle, or by sensing the expansion of the fuel injection line.
U.S. Pat. No. 3,511,088 of P. R. Weaver dated May 12, 1970 and entitled "Pressure Transducer and Timing System" discloses a timing system in which a pressure transducer is clamped to a fuel line to detect and signal the onset of fuel injection in response to expansion of the fuel line. U.S. Pat. No. 3,731,527 of Preston R. Weaver, dated May 8, 1973, and entitled "Fuel Injection Transducer and Timing System" discloses a transducer mounted at the fuel injection nozzle to detect the shock wave caused by the opening of the nozzle at the instant of fuel injection.
The deficiences of the prior art are particularly manifest either in restricting the fuel injection detection to only a single engine cylinder rather than all cylinders, which ultimately degrades the timing adjustment response time, or in requiring a separate detection device for each engine cylinder, thereby making the system expensive and complex. The prior art systems have additional problems in terms of providing detection means which accurately and reliably senses the fuel injection event over the normally wide range of engine operating characteristics and in the adverse fuel injection nozzle environment. THe devices which are integrally built into the injection nozzle structure are impractical and expensive.